1. Field of the Invention
The present invention relates to a fabrication method of a chip resistor of surface-mounting type.
2. Description of the Related Art
Recently, surface-mounting electronic devices have been widely used in order to improve the mounting density. FIG. 18 of the accompanying drawings shows a typical example of a conventional chip resistor. The resistor (generally indicated by the numeral 100) includes an insulating substrate 1, a first electrode 2a, a second electrode 2b, a resistive layer 3, an overcoat 4 and an undercoat 5. The first electrode 2a, identical to the second electrode 2b, is composed of an upper conductor 21a, an auxiliary conductor 21b, a lower conductor 22 and a side conductor 23.
A plurality of resistors 100 are produced efficiently by employing a collective production technique (whereby identical resistors are simultaneously obtained from a single mother substrate). Specifically, several elements, such as electrodes, resistive layers and protection covers, are prearranged on a common substrate. Then, the substrate is divided into smaller pieces along prescribed cut lines by a dicing cutter for example.
In accordance with the conventional method, however, it is difficult to cut the mother substrate properly, and unwanted burrs often result in the cut surface of the substrate, as will be described below.
Specifically, referring to FIGS. 19A and 19B, a mother substrate 10 is to be cut by a dicing cutter D. As illustrated, the substrate 10 is provided with a prescribed number of resistive layers 3, undercoats 5, overcoats 4, etc. The substrate 10 is fixed to an adhesive sheet 9 on a work table T. The adhesive sheet 9 is composed of a base 91 and an adhesive layer 92.
To cut the substrate 10, as shown in FIG. 19A, the dicing cutter D is urged downward by a certain pressure. Upon the pressure application, the dicing cutter D exerts a lateral force F (and forces of other directions) on the substrate 10. Conventionally, as the cutting proceeds and the local thickness of the substrate 10 is reduced to a certain value α (25 μm for example), the substrate 10 will be broken by the lateral force F, as shown in FIG. 19B. Though the substrate 10 is attached to the adhesive sheet 9, the sheet 9 is not strong enough to prevent the breakage of the substrate 10. Due to the improper cutting result, an unwanted burr 111a will be left at the cut surface of the conventional substrate.